They wanted a dream house. They got Hell House instead. “The Amityville Horror” is the now-infamous, “based on a true story” tale of the

Lutz family, who in 1975 bought a Long Island home that turned out, they claimed, to be haunted. While the parents, George and Kathy, later shared their version of events on the talk show circuit and elsewhere, their eldest son has a different tale — and he’s blaming it all on dad.

In “My Amityville Horror,” a documentary that opens on Friday, Daniel Lutz opens up about the events in the house for the first time. Daniel, who was 10 at the time, believes that George, his stepdad, invited mysterious and dangerous forces into their lives due to his interest in the occult.

Even before living in Amityville, Lutz recalls George talking about his interest in odd phenomena. He also says he once saw George levitate a wrench in the family’s garage.

“Danny was completely angry about not only the haunting, but his stepfather, and what he feels George did to the family,” says director Eric Walter, an Amityville-obsessive who’s been following the story since he was 12. “He feels that George triggered what happened.”

The Amityville tale began in 1974, when Ronald DeFeo Jr., 23, murdered his parents and four siblings in their home. The Lutzes, who knew the history, bought the house anyway, and reported bizarre phenomena from the outset.

A priest and family friend who had come to bless the house the day they moved in said that he heard a voice commanding him to leave, and was then slapped by a disembodied hand before fleeing the home.

Over the next month, they claimed to live through an unending demonic assault. At one point, Daniel said he saw 400-500 flies in one room, and killed about 100. When his parents went into the room, the flies were gone. Other family members experienced levitations and being touched by invisible forces. His sister reported seeing an angry pig with “wolflike teeth and laser beam red eyes.” Poltergeists were spotted in their boathouse, surrounded by green slime.

The family abandoned the house, leaving all their belongings behind. The tale became legend via a slew of books, films and media coverage.

Daniel, who paints his stepfather as a loveless drill sergeant, left home at 13 and seems to have never recovered from Amityville. He agreed to make the film because he wanted his story out, but he won’t speak to the press. He told Walter he would only tell his troubling tale once.

“It’s not easy to tell somebody how you got thrown up a staircase, or that your bed was bouncing off the ceiling ’cause the headboard posts were jammed into the Sheetrock,” Daniel says in the film, clearly disturbed by the memories. “The stench, black toilets, thousands of flies — like a f – – king carnival, man. I’m getting a little tight right now. This is not something I enjoy discussing.”

At 17, Walter founded amityvillefiles.com, a repository for facts and documents on the incident. He’s convinced the tale is not a hoax, in that the Lutzes genuinely believed that something mysterious occurred.

But he also feels that Daniel’s version has been colored by media coverage and hatred of his stepfather.

“In the 1979 film, Rod Steiger, who plays the priest, is attacked by a swarm of flies in the upstairs bedroom,” says Walter. “When I asked Danny about this, he told me he saw the priest run out the door, and that when he went to that bedroom, it was filled with 400, 500 flies. This sounds like the movie version. George and Kathy never claimed that this happened.”

Whatever the truth may be, Walter hopes that in giving Daniel his say, he can also provide him some peace.

“You’re looking at the dramatic psychological effect it had on this person,” Walter says. “That’s the real Amityville horror.”